The present invention relates to a method of registering a portable telephone unit included in a cordless telephone system, more particularly, a method of registering, on the master and slave units, a relationship allowing connection thereof.
It is a common practice with a cordless telephone system to write the same ID code in a master and a slave or portable unit at the time of shipment from a factory. In the event of communication, the master and slave units each sends the ID code together with a control signal, while the other executes processing only if the ID code included in the control signal is identical with the ID code stored therein. Although this kind of scheme is successful in eliminating erroneous connection, it has some issues yet to be solved, as follows.
A definite relation is set up, at the time of shipment, between the master and slave units as to whether or not they are permitted to be connected to each other, as mentioned above. Stated another way, it is impossible for a single slave unit to be selectively connected to a plurality of master units. This brings about a problem that a person is prevented from carrying the slave unit from, for example, a home to a relative's home, office or similar remote place and use it there. In this way, the conventional approach, assigning a single ID code to both the master and the slave units, is not practicable when it comes to a system wherein each slave unit is connectable to a plurality of master units. Therefore, it is necessary to assign a particular ID code to each of the master units and slave units, and to cause each unit to write therein the ID code of the other unit to which it is to be connected. Since no definite relations as to connectability can be set up between the master and the slave units at the time of shipment, it is necessary that each user can register, after shipment, a relation regarding connectability, i.e., the ID codes of the connectable master and slave units at each other.
For the registration of the ID codes, signals have to be interchanged between the master and the slave units over either a wired transmission path or a wireless or radio transmission path. An ID code setting method using a wired transmission path is disclosed in, for example, Japanese Patent Laid-Open Publication No. 2-309847. In this Laid-Open Publication, the transmission path is implemented by a charging line which is connected to the master and slave units via a terminal which is provided on the master unit for Charging the slave unit. The master unit is operated to set the ID codes. However, the problem with such a wired transmission path scheme is that a circuit for constructing an exclusive wired path for registration is needed which would increase the cost.
By contrast, a registering method using a radio transmission path can use radio communication functions originally incorporated in the master unit and slave unit and, therefore, does not need any extra circuit for registration. However, when the registration is simply performed on the master unit, as taught in the above-mentioned Laid-Open Publication, it is apt to be erroneous if some other slave units are awaiting registration in the neighborhood. Therefore, the prerequisite with the method using a radio transmission path is that the registration be sure and safe even when a plurality of pairs of master and slave units, which are located close to each other, are manipulated for registration at I the same time.